PS I don't have any add-ons or extensions except LocalFolders. Certainly nothing related to calendars or tasks that could add more complexity and trouble to shoot. Just a pure TB install.

perhaps look in the error console (ctrl+shift+J) for any error related to the storage file or the loading of the tasks.

It is always a good idea to try the troubleshooting mode on the help menu as well. While you don't have addons it disables more than that. It has also, for reasons that defy me, fixed problems permanently. Or so folk have reported.

troubleshooting mode did no good. The problem is worse today. There isn't even a left side bar with calendar icon, and settings has no calendar properties. At least I know one English word in the error console - "CORRUPTED".

1713248692600 addons.xpi WARN Checking C:\Program Files\Mozilla Thunderbird\distribution\extensions for addons Found 0 public keys and 0 secret keys (0 protected, 0 unprotected) RNPLib.jsm:559:15 NS_ERROR_FILE_CORRUPTED: Component returned failure code: 0x8052000b (NS_ERROR_FILE_CORRUPTED) [mozIStorageService.openDatabase] CalStorageDatabase.jsm:30 Calendar: Can't create calendar for cfc01f0a-a384-4f7d-ad06-5cb997eb2dfb (storage, moz-storage-calendar://): [Exception... "Component returned failure code: 0x8052000b (NS_ERROR_FILE_CORRUPTED) [mozIStorageService.openDatabase]" nsresult: "0x8052000b (NS_ERROR_FILE_CORRUPTED)" location: "JS frame :: resource:///modules/calendar/CalStorageDatabase.jsm :: openConnectionTo :: line 30" data: no] CalCalendarManager.jsm:535 Calendar: Can't create calendar for c2659364-df9b-4742-9a62-4cb1263e4477 (caldav, https://apidata.googleusercontent.com/caldav/v2/bob.infiniteventures%40gmail.com/events/): [Exception... "[JavaScript Error: "this.mOfflineStorage is null" {file: "resource:///modules/CalDavCalendar.jsm" line: 279}]'[JavaScript Error: "this.mOfflineStorage is null" {file: "resource:///modules/CalDavCalendar.jsm" line: 279}]' when calling method: [calIChangeLog::offlineStorage]" nsresult: "0x80570021 (NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS)" location: "JS frame :: resource:///components/calCachedCalendar.js :: calCachedCalendar :: line 124" data: yes] CalCalendarManager.jsm:535 NS_ERROR_FILE_CORRUPTED: Component returned failure code: 0x8052000b (NS_ERROR_FILE_CORRUPTED) [mozIStorageService.openDatabase] CalStorageDatabase.jsm:30 NS_ERROR_FILE_CORRUPTED: Component returned failure code: 0x8052000b (NS_ERROR_FILE_CORRUPTED) [mozIStorageService.openDatabase]

   openConnectionTo resource:///modules/calendar/CalStorageDatabase.jsm:30
   connect resource:///modules/calendar/CalStorageDatabase.jsm:116
   prepareInitDB resource:///modules/CalStorageCalendar.jsm:167
   set id resource:///modules/CalStorageCalendar.jsm:133
   setupCachedCalendar resource:///components/calCachedCalendar.js:205
   calCachedCalendar resource:///components/calCachedCalendar.js:122
   maybeWrapCachedCalendar resource:///modules/CalCalendarManager.jsm:985
   initializeCalendar resource:///modules/CalCalendarManager.jsm:218
   assureCache resource:///modules/CalCalendarManager.jsm:532
   getCalendars resource:///modules/CalCalendarManager.jsm:492
   set prefPrefix resource:///modules/CalCompositeCalendar.jsm:102
   getCompositeCalendar resource:///modules/calendar/utils/calViewUtils.jsm:133
   loadCalendarManager chrome://calendar/content/calendar-management.js:119
   loadCalendarComponent chrome://calendar/content/calendar-chrome-startup.js:55

calCachedCalendar.js:226:15 TypeError: this.mOfflineStorage is null CalDavCalendar.jsm:279:20 NS_ERROR_FILE_CORRUPTED: Component returned failure code: 0x8052000b (NS_ERROR_FILE_CORRUPTED) [mozIStorageService.openDatabase]